@jj253 , Ernestine, Even though the lights do come on, the battery could be low or bad connections, check for 12.2v+ at the battery,check connections on battery and follow them to their other end to ensure not corroded or loose. If need be try boosting. If truck starts, problem will be weak battery or bad connections.
When running if the battery is not showing 13.8+v, the alternator may be weak also.
If battery, connections, fuses/relays all look good, with foot on the brake, if automatic, shift out of park and try starting truck in neutral and other gears, this will maybe tell us if the safety neutral switch is out of adjustment, but could still be faulty, just as on a standard tranny the out of adj. or faulty clutch switch can cause this issue.
Now if able to access the starter give it a couple raps with a heavy object(hammer/metal bar) careful not to hit solenoid. After giving starter a couple good raps, try starting if it starts, the starter is sticking and faulty.
Now if the above had no effect and you can access the 2 large solenoid terminals and safely cross them out with a screw driver and truck still will not crank then the solenoid/starter are faulty.
Some of the auto parts suppliers offer free battery/starter/alternator testing, like Pepboys, Nappa, Advanced auto parts,etc and some of the guys are very knowledgeable and may have seen the issue often and put you on the right track. Good luck. I hope this helped you out, if so let me know by pressing the helpful button.